1. Field of the Invention
The invention relates to a microbiological process for the production of 6-hydroxypicolinic acid, starting from picolinic acid and/or its salts.
2. Background Art
Several methods for the production of 6-hydroxypicolinic acid by organic syntheses are known. From picolinic acid, for example, the 6-hydroxypicolinic acid can be obtained by reaction with potassium hydroxide [Tetrahedron Letters, Vol. 29, (1988), pages 4389 to 4392]. A drawback of such process is that the 6-hydroxypicolinic acid is obtained only in moderate yield (51 percent).
It is also known that microorganisms of genus Bacillus hydroxylate picolinic acid to 6-hydroxypicolinic acid [O. Shukla and S. M. Kaul, Indian J. of Biochemistry and Biophysics, Vol. 10, (1973), pages 176 to 178; O. Shukla et al., Indian J. of Biochemistry and Biophysics, Vol. 14, (1977), pages 292 to 295]. A great drawback of such process is that the further metabolization of the 6-hydroxypicolinic acid can be stopped only with the inhibitor sodium arsenite, and thus the growth of the microorganisms also is inhibited. Another drawback consists in that 6-hydroxypicolinic acid is not exclusively formed, but instead a mixture of 3,6-dihydroxypicolinic acid and 6-hydroxypicolinic acid is formed.
R. L. Tate and J. C. Ensign, Can. J. Microbiol., Vol. 20, (1974), pages 695 to 702, describes the hydroxylation of picolinic acid with microorganisms of genus Arthrobacter. Drawbacks of such process are that these microorganisms cannot exclusively use picolinic acid as a carbon, nitrogen and energy source, but in the hydroxylation, a yeast extract has to be present, which can lead to undesirable impurities of the product. Another drawback lies in the fact that the 6-hydroxypicolinic acid is formed only in the case of low oxygen content, and the microorganisms are not present in the growth phase, and thus little product is formed.